doc: git-rebase: move --onto explanation down

There's a very clear explanation with examples of using --onto which is
currently buried in the very long DESCRIPTION section. This moves it to
its own section, so that we can reference the explanation from the
`--onto` option by name.

Signed-off-by: Julia Evans <[email protected]>

Author: jvns

Documentation/git-rebase.adoc

@@ -114,87 +114,6 @@ will result in:
     D---E---A'---F master
 ------------
 
-Here is how you would transplant a topic branch based on one
-branch to another, to pretend that you forked the topic branch
-from the latter branch, using `rebase --onto`.
-
-First let's assume your 'topic' is based on branch 'next'.
-For example, a feature developed in 'topic' depends on some
-functionality which is found in 'next'.
-
-------------
-    o---o---o---o---o  master
-         \
-          o---o---o---o---o  next
-                           \
-                            o---o---o  topic
-------------
-
-We want to make 'topic' forked from branch 'master'; for example,
-because the functionality on which 'topic' depends was merged into the
-more stable 'master' branch. We want our tree to look like this:
-
-------------
-    o---o---o---o---o  master
-        |            \
-        |             o'--o'--o'  topic
-         \
-          o---o---o---o---o  next
-------------
-
-We can get this using the following command:
-
-    git rebase --onto master next topic
-
-
-Another example of --onto option is to rebase part of a
-branch.  If we have the following situation:
-
-------------
-                            H---I---J topicB
-                           /
-                  E---F---G  topicA
-                 /
-    A---B---C---D  master
-------------
-
-then the command
-
-    git rebase --onto master topicA topicB
-
-would result in:
-
-------------
-                 H'--I'--J'  topicB
-                /
-                | E---F---G  topicA
-                |/
-    A---B---C---D  master
-------------
-
-This is useful when topicB does not depend on topicA.
-
-A range of commits could also be removed with rebase.  If we have
-the following situation:
-
-------------
-    E---F---G---H---I---J  topicA
-------------
-
-then the command
-
-    git rebase --onto topicA~5 topicA~3 topicA
-
-would result in the removal of commits F and G:
-
-------------
-    E---H'---I'---J'  topicA
-------------
-
-This is useful if F and G were flawed in some way, or should not be
-part of topicA.  Note that the argument to `--onto` and the `<upstream>`
-parameter can be any valid commit-ish.
-
 MODE OPTIONS
 ------------
 
@@ -240,6 +159,8 @@ As a special case, you may use "A\...B" as a shortcut for the
 merge base of A and B if there is exactly one merge base. You can
 leave out at most one of A and B, in which case it defaults to HEAD.
 
+See TRANSPLANTING A TOPIC BRANCH WITH --ONTO below for examples.
+
 --keep-base::
 	Set the starting point at which to create the new commits to the
 	merge base of `<upstream>` and `<branch>`. Running
@@ -1018,6 +939,91 @@ consistent (they compile, pass the testsuite, etc.) you should use
 after each commit, test, and amend the commit if fixes are necessary.
 
 
+TRANSPLANTING A TOPIC BRANCH WITH --ONTO
+----------------------------------------
+
+Here is how you would transplant a topic branch based on one
+branch to another, to pretend that you forked the topic branch
+from the latter branch, using `rebase --onto`.
+
+First let's assume your 'topic' is based on branch 'next'.
+For example, a feature developed in 'topic' depends on some
+functionality which is found in 'next'.
+
+------------
+    o---o---o---o---o  master
+         \
+          o---o---o---o---o  next
+                           \
+                            o---o---o  topic
+------------
+
+We want to make 'topic' forked from branch 'master'; for example,
+because the functionality on which 'topic' depends was merged into the
+more stable 'master' branch. We want our tree to look like this:
+
+------------
+    o---o---o---o---o  master
+        |            \
+        |             o'--o'--o'  topic
+         \
+          o---o---o---o---o  next
+------------
+
+We can get this using the following command:
+
+    git rebase --onto master next topic
+
+
+Another example of --onto option is to rebase part of a
+branch.  If we have the following situation:
+
+------------
+                            H---I---J topicB
+                           /
+                  E---F---G  topicA
+                 /
+    A---B---C---D  master
+------------
+
+then the command
+
+    git rebase --onto master topicA topicB
+
+would result in:
+
+------------
+                 H'--I'--J'  topicB
+                /
+                | E---F---G  topicA
+                |/
+    A---B---C---D  master
+------------
+
+This is useful when topicB does not depend on topicA.
+
+A range of commits could also be removed with rebase.  If we have
+the following situation:
+
+------------
+    E---F---G---H---I---J  topicA
+------------
+
+then the command
+
+    git rebase --onto topicA~5 topicA~3 topicA
+
+would result in the removal of commits F and G:
+
+------------
+    E---H'---I'---J'  topicA
+------------
+
+This is useful if F and G were flawed in some way, or should not be
+part of topicA.  Note that the argument to `--onto` and the `<upstream>`
+parameter can be any valid commit-ish.
+
+
 RECOVERING FROM UPSTREAM REBASE
 -------------------------------